1. Field of the Invention
The present invention relates generally to pharmaceutical compositions that include paclitaxel derivatives and methods for preparing and using stent devices to make them resistant to overgrowth by inflammatory and fibrous scar tissue.
2. Description of the Related Art
The clinical function of numerous medical implants and devices is dependent upon the device being able to effectively maintain an anatomical, or surgically created, space or passageway. Unfortunately, many devices implanted in the body are subject to a “foreign body” response from the surrounding host tissues. In particular, injury to tubular anatomical structures (such as blood vessels, the gastrointestinal tract, the male and female reproductive tract, the urinary tract, sinuses, spinal nerve root canals, lacrimal ducts, Eustachian tubes, the auditory canal, and the respiratory tract) from surgery and/or injury created by the implantation of medical devices can lead to a well known clinical problem called “stenosis” (or narrowing). Stenosis occurs in response to trauma to the epithelial lining or the entire body tube during the procedure, including virtually any manipulation which attempts to relieve obstruction of the passageway, and is a major factor limiting the effectiveness of invasive treatments for a variety of diseases to be described later.
Stenosis (or “restenosis” if the problem recurs after an initially successful attempt to open a blocked passageway) is a form of response to injury leading to wall thickening, narrowing of the lumen, and loss of function in the tissue supplied by the particular passageway. Physical injury during an interventional procedure results in damage to epithelial lining of the tube and the smooth muscle cells (SMCs) that make up the wall. The damaged cells, particularly SMCs, release cytokines, which recruit inflammatory cells such as macrophages, lymphocytes and neutrophils (i.e., which are some of the known white blood cells) into the area. The white blood cells in turn release a variety of additional cytokines, growth factors, and tissue degrading enzymes that influence the behavior of the constituent cells of the wall (primarily epithelial cells and SMCs). Stimulation of the SMCs induces them to migrate into the inner aspect of the body passageway (often called the “intima”), proliferate and secrete an extracellar matrix—effectively filling all or parts of the lumen with reactive, fibrous scar tissue. Collectively, this creates a thickening of the intimal layer (known in some tissues as “neointimal hyperplasia” that narrows the lumen of the passageway and can be significant enough to obstruct its lumen.